| Surface plasmon resonance (SPR) is a spectroscopy that measures the response of a surface wave at the interface of a conductor and a dielectric, called the surface plasmon polariton (SPP). In the Kretschmann configuration, a thin film of the conductor is illuminated under total internal reflection via a prism. At the appropriate angle and frequency, an absorption is seen in reflected p-polarized light. This excitation is highly sensitive to the properties of the dielectric medium, the conductor itself, and the substrate material.;Theoretical modeling is valuable in SPR, because of the high sensitivity and the large number of experimental variables involved. As the technology advances, increasingly sophisticated modeling techniques become necessary. In addition, with the aid of theoretical modeling, SPR may be used as a materials characterization tool, to study the properties of the conductors themselves.;In this dissertation, several plasmonic systems were studied. First, in chapters 2 and 3, films of silver sandwiched between two layers of non-conductive aluminum-doped zinc oxide (AZO) on glass were considered. The films were prepared by reactive pulsed DC magnetron sputtering, and the silver thickness was varied. The films' SPR response was measured in the near-IR in air. Theoretical modeling of Rp/Rs was performed by the multilayer transfer-matrix method, with the aid of a modified Nelder-Mead simplex optimization algorithm. The initial modeling results suggested that both the silver and AZO properties were significantly different from the bulk materials. In particular, the silver had a higher plasma frequency and high-frequency dielectric constant than bulk, and it was hypothesized that the AZO was contributing charge carriers into the silver layer. However, upon review it was determined that a miscalibration of the incident angles could also explain the results.;Second, in chapter 4, films of silver sandwiched between two layers of AZO were deposited using pulsed laser deposition (PLD) onto both glass and CaF2. The film thicknesses were held nearly constant, and the AZO plasma frequency was varied by changing the Al doping concentration and oxygen pressure during deposition. The films' SPR response was measured in near-IR in two separate instruments, in air for the films on glass and in water for the films on CaF2. In the theoretical modeling, which took place via the multilayer transfer-matrix model, the bulk silver dielectric function was used, and the AZO dielectric function was approximated as a hybrid between a conductive Drude model and the ZnO bulk. Initial results were promising, but indicated that the system was limited by the accuracy of the film thickness measurements and the consistency of the deposition process.;Third, in chapter 5, pure AZO films were assessed using SPR spectroscopy. The films were deposited using PLD in an oxygen environment onto CaF 2. The SPR responses of the films were measured in both air, in the near-IR, and in water, in the mid-IR. A modified Nelder-Mead simplex optimization algorithm was used to determine the optical constants of the films in the Drude model. The high-frequency dielectric constant was consistent with literature values. However, the plasma frequency and damping constant suggested that the films had a higher free electron mass than is reported in the literature. In addition, the spectra in water were complex, which was explained as the result of interaction of the water molecular vibrations with the surface plasmon polariton in the mid-IR. This is believed to be the first reported observation of a mid-IR water-plasmon interaction in this fashion. |
